1. Field of the Invention
The present invention relates to a cartridge engaging mechanism for the engagement between a tape cartridge and a tape drive device when the tape cartridge is loaded into the tape drive device.
2. Description of the Related Art
A single reel cartridge magnetic tape is used as one of storage media for computers. The magnetic tape is wound around a reel while one end thereof is fixed to the core of the reel, and the reel is supported in a case of a cartridge so as to be rotatable relatively to the case. The other end of the magnetic tape is drawn out from the case of the cartridge followed by rotation of the reel.
When the cartridge is loaded in the magnetic tape drive device, the rotational driving force can be transmitted from the driving motor (reel motor) of the drive device to the reel of the cartridge by a cartridge engaging mechanism. In order to construct the cartridge engaging mechanism, a plane-type cartridge gear exposed to the outside from the outer surface of the case is equipped to the reel at the cartridge side, and a plane-type drive gear for receiving the rotational force transmitted from the reel motor is disposed at the drive device side, and the cartridge gear and the drive gear are disposed so as to come into contact with each other and separate from each other.
The cartridge is equipped with a reel lock mechanism for preventing the reel from being rotated relatively to the case of the cartridge when the cartridge is unloaded from the drive device (that is, the engagement of the cartridge engaging mechanism is canceled). With the reel lock mechanism, the reel can be prevented from being rotated relatively to the case of the cartridge under states other than the loading state of the cartridge in the drive device, thereby preventing rewinding of the magnetic tape and occurrence of slack of the magnetic tape.
The reel lock mechanism is designed so that brake is released only when the cartridge gear is engaged with the drive gear. In order to satisfy this operation, a movable member called as a lock pad which abuts against the gear tooth tops of the drive gear is secured to each portion at which some gear teeth are removed from the cartridge gear. The lock pad is disposed so as to be reciprocatively movable between an advance position at which the lock pad is projected forwardly from the gear surface and a retraction position at which the lock pad is retracted backwardly from the gear surface. The lock pad is forwardly urged to the advance position by a spring. The brake acts at the advance position, and the lock pad is backwardly moved to the retraction position against the urging force of the spring to release the brake. Therefore, the lock pad is required to have a proper reciprocative movement stroke.
FIG. 12 is a schematically partially cross-sectional view showing the drive gear and the cartridge gear of a conventional cartridge engaging mechanism as described above.
A cartridge gear 101a is designed in an annular form so as to surround the rotational center CL1 extending in the up-and-down direction, and three lock pads 101b are disposed so as to be spaced at an equal angular interval in the circumferential direction of the cartridge gear 110a. Each lock pad 101b is movable in the up-and-down direction over a required stroke with the position shown in FIG. 12 as the lower limit position. A non-tooth portion 101e at which three gear teeth of the cartridge gear 101a are removed is formed in the neighborhood of the formation position of each lock pad 101b. The drive gear 122 has such a shape that it is fit to the cartridge gear 101a, and it is designed in an annular form so as to surround the rotational center CL2 extending in the up-and-down direction.
Each tooth top of the cartridge gear 101a is provided with a tapered portion having a gradually-lowered taper angle of xcex8a in an area extending inwardly from each lock pad 101b, and each tooth top of the drive gear 122 is provided with a tapered portion having a gradually-lowered taper angle of xcex8b in an area extending inwardly from the center of each lock pad 101b as shown in FIG. 12. Accordingly, under the state that the cartridge gear 101a and the drive gear 122 are properly engaged with each other with the rotational centers CL1, CL2 thereof being common to each other, the tooth tops of the drive gear 122 abut against and pushes the lock pads 101b at the highest position of the tooth tops, so that the lock pads 101b can be moved by a distance enough to release the brake.
However, if the precision of the positioning of the cartridge case to the drive device when the cartridge is loaded into the drive device and the positional precision of the cartridge gear to the cartridge case are not sufficient, there occurs a positional error between the cartridge gear 101a and the drive gear 122 as shown in FIG. 13. As shown in FIG. 13, there is a case where the positional error described above occurs so that the positional error direction of the cartridge gear 101a with respect to the drive gear 122 is substantially coincident with the direction of the lock pad 101b relative to the rotational center CL1 of the cartridge gear 101a. 
FIG. 14 is a cross-sectional view in the circumferential direction showing the neighborhood of the position corresponding to the lock pads 101b at the outermost peripheral position at which the tooth tops of the drive gear 122 are highest.
As is apparent from FIG. 14, when a slight inclination occurs between the rotational axis direction of the drive gear 122 and the rotational axis direction of the cartridge gear 101a, the tooth tops at both sides of each non-tooth portion 101e intrude in each portion having the largest tooth top pitch in the neighborhood of the outermost peripheral portion of the drive gear 122. Firstly, this is because the tooth top pitch of the cartridge gear 101a is smaller than the tooth top pitch of the drive gear 122 within the cross section shown in FIG. 14, and secondly this is because the tooth tops of the drive gear 122 are formed to be highest in height in order to achieve a required lock pad movement stroke, so that the width Wxe2x80x2 of the flat portion of each tooth top of the drive gear 122 is small and thus there is little margin in receiving the tooth tops of the cartridge gear 101a by the flat portions of the tooth tops of the drive gear 122. Under such a situation, the relative rotation between both the gears is impossible, and thus it is impossible to properly engage both the gears with each other.
Therefore, in the conventional cartridge engaging mechanism, the permissible dimension for the error or displacement Sxe2x80x2 between the rotational centers CL1, CL2 of the gears which enables the proper engagement between both the gears is reduced, and thus it is required to enhance the precision of the positioning of the cartridge case to the drive device and also enhance the positional precision of the cartridge reel to the cartridge case. This is an obstacle to reduce the cost of the cartridge engaging mechanism and the cartridge and drive device.
An object of the present invention is to enhance the tolerance level of the positional error between a cartridge gear and a drive gear to be engaged with each other in a cartridge engaging mechanism.
Another object of the present invention is to enhance the tolerance level of the positional error between a cartridge gear and a drive gear to be engaged with each other in a cartridge engaging mechanism while keeping a required movement stroke of a lock pad of a reel lock mechanism.
In order to attain the above object, according to the present invention, there is provided a cartridge engaging mechanism for engaging a plane-type cartridge gear secured to a reel of a tape cartridge loaded in a tape drive device with a plate-type drive gear connected to a reel motor of the tape drive device, characterized in that the cartridge gear has a tapered shape having a first inclination angle that is lower in height as the tooth tops thereof approach to the innermost peripheral edge, and the drive gear has a tapered shape having a second inclination angle that is lower in height as the tooth tops thereof approach the outermost peripheral edge, the second inclination angle being set to be smaller than the first inclination angle.
In an aspect of the present invention, each of a face of the cartridge gear and a face of the drive gear is formed in an annular shape in a peripheral direction around a rotational center thereof.
In an aspect of the present invention, the cartridge is equipped with a reel lock mechanism for preventing rotation of the reel with respect to a case of the cartridge, and the reel lock mechanism has a lock pad that is reciprocatively movable between an advance position and a retract position at a part of the face of the cartridge gear and urged toward the advance position.
In an aspect of the present invention, the tapered shape of the drive gear is formed in an area which extends outwardly from the radially-innermost position of the drive gear at which the lock pad abuts against the drive gear under the state that the drive gear and the cartridge gear are in proper engagement with each other. In an aspect of the present invention, a width of a flat portion of each of the tooth tops of the drive gear is gradually larger in the outward direction from the radially-innermost position of the drive gear at which the lock pad abuts against the drive gear under the state that the drive gear and the cartridge gear are in proper engagement with each other.
In an aspect of the present invention, the tapered shape of the cartridge gear is formed in an area which extends inwardly from the innermost position of the lock pad in the radial direction of the cartridge gear. In an aspect of the present invention, the cartridge gear has a non-tooth portion having no tooth in an area in the neighborhood of the lock pad.
In an aspect of the present invention, the cartridge engaging mechanism further comprises urging means for urging the cartridge gear toward said drive gear. In an aspect of the present invention, the urging means comprises a magnet equipped to the drive gear and a magnetic member equipped to the cartridge gear.
In an aspect of the present invention, a case of the tape cartridge is equipped with a positioning hole, and the tape drive device is equipped with a support pin which is inserted into the positioning hole when the cartridge gear is engaged with the drive gear to position the case to the tape drive device. In an aspect of the present invention, the support pin has such a sufficient length as to be inserted into the positioning hole before contact between the cartridge gear and the drive gear is started when the cartridge gear is engaged with the drive gear.
According to the present invention, the tolerance level of the positional displacement between the cartridge gear and the drive gear to be engaged with each other in the cartridge engaging mechanism can be enhanced by the specific shape of the teeth of the drive gear, and particularly the tolerance level of the positional displacement between the cartridge gear and the drive gear can be enhanced while keeping the required movement stroke of the lock pads of the reel lock mechanism.